This invention relates to a production line for bitumen cakes.
Oxidized bitumen is a peculiar amorphous material which is generally in liquid form when discharged by oxidation plants at a temperature ranging from 240.degree. to 300.degree. C., and becomes solid or pasty at ambient temperatures. While being relatively hot, it is viscous, whereas when in pasty or solid state it possesses a fair degree of elasticity. Both in liquid and in plastic or solid form oxidized bitumen is a highly insulating material with good ahesion properties with respect to almost any solid material.
It is known to produce oxidized bitumen cakes or pigs by casting a mass of liquid bitumen directly into bags formed from a special paper variety and being held within suitable containers which perform the function of molds for the bitumen being solidified in the paper bags. Other methods currently practiced provide for direct casting of hot bitumen into suitable cardboard drums.
These methods suffer all serious drawbacks in that casting in paper bags or cardboard drums must occur at relatively low temperatures to prevent the package from being damaged. At relatively low casting temperature oxidized bitumen becomes highly viscous and any metering, pumping or casting equipment is liable to become clogged or difficult to operate. Moreover, paper bags are sometimes damaged or defective, which results in hot bitumen being spilled on the floor and possibly on the personnel feet.
On the other hand, when bitumen cakes packaged in paper or cardboard are removed from a storing place after relatively long storing time intervals for being melted and used by the consumer, paper or cardboard is often found to be at least partly incorporated in the bitumen cake. Paper hardly peels off from bitumen cakes, remains in the bitumen and must be removed later on by skinning the bitumen once melted.
Also known is to cast hot liquid bitumen into metal containers or molds having a vertical main dimension (i.e. very deep and narrow), which include several component parts and have a bottom which can be opened. Such containers are intended for receiving fluid hot bitumen and serving as solidification molds for the bitumen poured therein while being cooled either through elongate water tanks or through a forced ventilation tunnel. As they emerge out of the cooling tanks or tunnel, the formed bitumen cakes are removed from the containers and then packaged in paper bags or drums.
However, metal composite molds, i.e. molds with removable or movable portions, have some serious disadvantages both from a tehnical standpoint and of the investment involved in their manufacture and installation and of the system maintenance costs. In so far as the technical aspect is concerned, experience has shown that currently used metal molds having movable portions are liable to frequent failures that affect the production output in a drastic way and require very long water cooling lines, which are accordingly very expensive and cumbersome, and thus they occupy large floor areas.
A mold, that has to be opened, cannot be a tight container and thus leaks of liquid bitumen may occur owing to unavoidable clearance between movable components of the mold. Furthermore, when the molds are immersed in a water tank for cooling purposes the hydrostatic thrust is responsible for causing water to leak thrugh the gap between the movable components of the mold and may become incorporated in the liquid bitumen bitumen contained in the mold. This water is subsequently responsible for undesirable formation of foam when bitumen cakes are remelted before bitumen is used.
In addition, even composite molds of more recent design present serious shake-out problems in that the cakes cooled within the metal containers cannot be removed in spite of the action of ultrasound, infrared beams, and mechanical ejectors having been utilized. Frequently, breakage of the metal container occurs before the bitumen cake solidified therein can be shaken out by the ejector.